Truncate the size of the document combo to allow the symbol combo to still be clearly visible when the window is made smaller. It is possible that the document combo will have a lot of blank space which it is not needing and this causes the symbol combo to not be visible, specifically the drop down arrow is not visible. So making adjustments to use the area more efficiently will at least make it possible to show something so that it can be chosen.

This is easy to notice on macOS when you resize the width of the window to be the smallest possible, the symbol combo is no longer visible.